Industrial vehicles such as forklift trucks, end-riders, center-riders, pallet trucks, walkies, and the like, may include a pair of forks configured to engage a pallet. The pallet may include one or more openings into which the forks are inserted prior to moving the pallet, and each opening may include upper and lower surfaces that provide stability to the pallet. For example, the upper surface and/or the lower surface of each opening may include one or more boards extending the width of the pallet. The forks may be inserted between the upper surface and the lower surface. An empty pallet may tend to slide across the floor during insertion of the forks into the opening(s) when one of the forks contacts the upper surface and/or the lower surface of the pallet, such as when the height of the forks is uneven.
Certain types of industrial vehicles, such as pallet trucks with fixed linkages for raising and lowering the forks, are known to have uneven fork heights and/or non-level fork surfaces due to manufacturing tolerances that may cause one fork to be either higher or lower relative to the other. The non-level forks may result in uneven lifting and lowering, and vehicles having non-level forks may tend to rock back and forth or transfer weight between the forks, such that only one load wheel may be in contact with the ground at any point in time. The effects of the uneven forks may be more pronounced when there is no load on the forks.
While fixed linkage fork elevation systems may be relatively uncomplicated and include a small number of component parts, these systems may be susceptible to tolerance stack up between the components, which may result in non-level fork surfaces. Additionally, components such as pull rods and other linkage components may require specific model matching to limit manufacturing error, which may complicate service and maintenance operations due to the part matching requirements. In some instances, a manufacturer may expend time and resources either straightening or bending the structure to get the forks to lie more evenly on the load wheels.
Some known pallet trucks have attempted to provide for adjustment of the fork height by varying the length of a pull rod. For example, an adjustment mechanism is described in U.S. Pat. No. 7,191,872 as being located at the rear of the pull rod, next to the truck frame. However, these types of known adjustment mechanisms may create bending and/or tensile forces on the pull rod as a result of the adjustment process and ensuing usage of the forks at the adjusted pull rod length, which can lead to premature failure or require additional maintenance be performed. Additionally, known adjustment mechanisms located at the rear of the pull rod typically are only accessible from underneath the forks, which may require that the forks and/or entire pallet truck be raised off the ground a sufficient distance to provide user access.